Investigators at Rocky Mountain Laboratories have recently discovered a spirochete in Ixodes dammini, I. pacificus, and I. ricinus ticks (see Project No. Z01 AI 00268-0l EB by Dr. Willy Burgdorfer). We have demonstrated high concentrations of antibodies to a strain of I. dammini-associated spirochete in the blood of patients with Lyme disease or erythema chronicum migrans. We are studying the biology of these spirochetes and the relationship between them and Lyme disease. We have to date: (l) formulated a cell-free medium for in vitro cultivation of these spirochetes; (2) isolated and propagated spirochetes from both I. dammini and I ricinus; (3) raised both polyclonal antisera and monclonal antibodies against an I. dammini-associated spriochete; and (4) identified major spirochetal antigens to which Lyme disease patients form antibody.